Blood and immunity: type I hypersensitivity: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Blood and immunity: type I hypersensitivity

Sample item

Within minutes of a wasp sting, a man develops urticaria, wheeze and hypotension. Which immune mechanism accounts for these features?

AAllergen cross-links IgE bound to mast cells, releasing histamineBImmune complexes deposit in vessel walls and activate complementCAntibodies coat cells and lead to complement-mediated lysisDSensitised T cells release cytokines over 48 to 72 hours

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Allergen cross-links IgE bound to mast cells, releasing histamine

In type I hypersensitivity, pre-formed IgE bound to FcepsilonRI on mast cells and basophils is cross-linked by allergen. Degranulation releases histamine and other mediators within minutes, producing urticaria, bronchospasm and hypotension. Types II, III and IV have different effectors and timing.

Option by option

A. Allergen cross-links IgE bound to mast cells, releasing histamine (correct)
Correct. IgE cross-linking on mast cells degranulates them within minutes.
B. Immune complexes deposit in vessel walls and activate complement
Immune complex deposition is type III and takes days to develop.
C. Antibodies coat cells and lead to complement-mediated lysis
Antibody-coated cell lysis describes type II reactions.
D. Sensitised T cells release cytokines over 48 to 72 hours
A T-cell reaction peaking in 48 to 72 hours describes type IV delayed hypersensitivity.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, Allergen cross-links IgE bound to mast cells, releasing histamine. In type I hypersensitivity, pre-formed IgE bound to FcepsilonRI on mast cells and basophils is cross-linked by allergen.

Why is "Immune complexes deposit in vessel walls and activate complement" not the answer?

Immune complex deposition is type III and takes days to develop.

Why is "Antibodies coat cells and lead to complement-mediated lysis" not the answer?

Antibody-coated cell lysis describes type II reactions.

Why is "Sensitised T cells release cytokines over 48 to 72 hours" not the answer?

A T-cell reaction peaking in 48 to 72 hours describes type IV delayed hypersensitivity.

What concept does this question test?

It tests Blood and immunity: type I hypersensitivity in Physiology. Degranulation releases histamine and other mediators within minutes, producing urticaria, bronchospasm and hypotension. Types II, III and IV have different effectors and timing.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Blood and immunity: type I hypersensitivity?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.